Microbial influence on the accumulation of Precambrian aeolian deposits (Neoproterozoic, Venkatpur Sandstone Formation, Southern India)

• Published in: Precambrian research 2020-09, Vol.347, p.105854, Article 105854
• Main Authors: Basilici, Giorgio, Soares, Marcus Vinicius Theodoro, Mountney, Nigel Philip, Colombera, Luca
• Format: Article
• Language: English
• Subjects: Aeolian depositional systems; India; Microbially induced sedimentary structures (MISS); Neoproterozoic; Venkatpur Sandstone Formation
• ISSN: 0301-9268; 1872-7433
• DOI: 10.1016/j.precamres.2020.105854

[Display omitted] •Although the occurrence of a potential large amount of sand source, the Venkatpur aeolian system did not generate an erg.•Water and microbial mat restricted the sand availability, essential for construction of an erg.•The interaction of wind and microbial-mat growth formed biolaminites.•Microbial mats, acting as an important stabilising agent, allowed the progressive and gradual vertical accumulation of sand. In many presently active aeolian systems, processes of sediment erosion, transport and deposition are markedly influenced by vegetation, which acts as an important sediment stabilising agent. Current sedimentary models for hyperarid continental settings devoid of vegetation and with adequate sand supply and wind force envisage intense aeolian activity, resulting in the construction of extensive aeolian sand-seas (ergs). During the Proterozoic, the Earth’s surface was devoid of vegetation, yet ergs are not so common in Proterozoic continental successions. High water-table levels, and erosional reworking by fluvial or marine processes are recognised as possible factors that restricted accumulation and preservation of extensive Proterozoic aeolian systems. By contrast, Proterozoic biotic communities have traditionally been considered largely incapable of markedly influencing clastic sedimentary processes in continental settings. However, since it is now known that bacteria have colonised parts of the continental Earth's surface since the Palaeoarchean, a question arises as to whether such organisms might have exercised some control on aeolian processes via substrate stabilisation. The Neoproterozoic Venkatpur Sandstone Formation (maximum age 709 Ma) is an aeolian depositional unit comprising small, isolated barchanoid and transverse dunes, and dry and damp sand sheet palaeoenvironments. Water-table-influenced aeolian sand-sheet deposits composed of thin sand layers that alternate with a suite of microbially induced sedimentary structures (MISS) provide evidence for fossilised bacteria. These strata record the interaction between microbial mats and aeolian depositional processes, which enabled the construction and accumulation of sand deposits. As microbial mats stabilised and provided plasticity to the depositional accumulation surface, they protected underlying (i.e. accumulated) aeolian deposits from possible wind erosion, reducing the possibility that these stored deposits could be recycled as lagged input to a downwind aeolian syst